A camera is a device for capturing images. A traditional camera uses film and photographic paper as the capture medium. More recently, the electronic camera has been invented that permits the capture of images in electronic form, principally as files that can be read, processed and displayed by other electronic devices.
An electronic camera comprises two principal components. These are an optical train and an image sensor. The optical train typically contains a plethora of optical active elements including, but not limited to baffles, lenses, apertures, stops, mirrors and the alike. The function of the optical train is to capture light from the scene of interest and focus it on to the image sensor with high fidelity. That is, without too much distortion, aberration, blurring, ghosting or any of the multiplicity of optical artefacts that are known and which serve to degrade the fidelity of the captured image. The image sensor is an electro-optic component, commonly made of silicon. The operation of such components typically involves dividing the focused image into a large number of microscopic portions and recording the colour and illumination intensity of each. The image sensor then processes this information to output a representation of the image in an electronic form. Often these forms are defined by Standards, such as JPEG, permitting them to be readily processed and displayed by other electronic devices.
Electronic cameras come in essentially two flavours. These are fixed optic and variable optic. In a fixed optic camera all the elements of the optical train are fixed in functionality and location in the camera at the time of manufacture. This means the performance of the optical train and hence the camera is invariant. Because the primary function of any camera is to capture focused images, cameras of this type are often referred to as ‘fixed focus’. Typically the focus of a fixed focus camera is set at about 1.2 m from the camera. This means that all objects in the range from 60 cm to many tens of metres away have acceptable fidelity in the captured image. In a variable optic camera, one or more elements of the optical train may be designed to permit variation in function, functionality or location. For example an aperture placed at the front of an optical train has a major influence on the quantity of light that reaches the image sensor and hence the brightness or darkness of the resulting image. By suitable adjustment of the aperture, one camera can produce images of good fidelity in conditions where the scene is brightly lit, for example in bright sunshine, and where it may be dimly lit, for example in moonlight.
Another example of a variable optic camera is one wherein the position of the entire optical train can be moved along the optical axis of the camera. This alters the focus of the camera permitting objects that are almost any distance from the camera to be captured with high fidelity. If the camera operator selects the focus distance by manual adjustment of the position of the optical train the camera is said to be ‘manual focus’. Where an electronic system is used to measure the distance from the camera of the objects in the scene and is used in conjunction with an actuator to move the optical train, the camera is said to be ‘auto focus’.
It has been found possible to combine many functions in a variable optic camera. Thus, for example, it is possible to purchase a camera that has simultaneous autofocus and zoom capability. However combination of functions like this inevitability results in an optical train of considerable complexity and consequentially size, weight, cost and poor reliability. Consequently improvements in autofocus zoom cameras are desirable and particularly for miniature cameras that are incorporated in portable electronics products such as mobile phones.